An important field of application, in which the invention shows itself to its best advantage, is the production of laminate floor panels of the DPL type (Direct Pressure Laminate). Such floor panels mostly are realized by first producing large board-shaped elements of DPL and subsequently sawing those to form floor panels, which then are provided with coupling profiles at their edges. As is known, the board-shaped elements of DPL generally are realized by mutually consolidating, on the one hand, one or more resin-treated material sheets, amongst which a printed decor layer, and, on the other hand, a substrate, whether or not formed of several layers or parts, by means of a press treatment, under the influence of pressure and temperature.
As further will become clear from the following description, the invention also shows itself to its best advantage in applications, wherein, during performing the press treatment, impressions are also formed in the decorative side of the board-shaped material, which have to be in register with the applied decor. This technique, which is called “embossed in register”, is known, amongst others, from the patent document WO 01/96689.
When producing the aforementioned floor panels, it is known that, for performing said press treatment, use is made of large press elements, consisting of one-piece press plates, with which the aforementioned board-shaped material is pressed. Mostly, these press plates, which are also called “platens”, are having dimensions in the order of magnitude of 2.5×5 meters and a thickness of approximately 0.5 cm or more.
Applying large press plates has the advantage that a rather large surface can be processed in one press treatment, in other words, in one press treatment a board-shaped element can be processed, which is of such dimensions that a plurality of floor panels, mostly 10 to 30, can be made from it. Another advantage of the use of such large press plates consists in that better yields are obtained in respect to the energy consumption for heating the presses than in the case that, for example, smaller plates in smaller presses were applied.
However, the application of the known large press plates also has different disadvantages.
A disadvantage consists in that, when such large press plate is damaged locally, for example, by scratching or the like, it must be replaced completely. Replacing such press plate is rather expensive, on the one hand, because the press plate itself costs a lot, and on the other hand also because of the transport costs, in view of the fact that the production of such large press plates takes place exclusively at specialized companies, which often are situated at distant locations.
Also, due to the fact that up to now such large press plates are produced by specialized companies, the disadvantage is created that the communication between the designer of a decor, who mostly is resident at the floor panel manufacturer's, and the producer of the press plates, who often is situated at a distant location, regularly is quite difficult. In view of the fact that often, the press plates are provided with a relief which must be in register with the decor, a good communication is very important. In order to remedy this disadvantage, one might consider integrating facilities for manufacturing press plates into a production unit for floor panels, such that a smoother communication becomes possible. However, due to the proportions of the known large press plates, expensive equipment is necessary for manufacturing them, for example, for etching the surface of such press plates, and up to now, performing such integration is not worthwhile. In fact, such integrated equipment would be in use only now and then, namely each time a new press plate must be produced, which would only lead to a low yield in respect to the utilization of the equipment and in respect to the input of specialized personnel.
Another disadvantage of such large one-piece press plates consists in that, when these must be provided with a relief, for example, an etched texture or etched pattern, it is rather difficult to perform such texture or such pattern faultless over the entire surface. In the case of an unacceptable deviation, a new press plate must be produced. Also, with large surfaces it is difficult to maintain high resolutions when etching. Moreover, it is difficult to etch large surfaces in a uniform manner. When etching large surfaces, a number of actions still must be performed manually, which requires particular skill.
In the case that one is working with press plates having a relief with which impressions must be realized that have to be in register or approximately in register with a decor present on a decor paper to be pressed or the like, still another disadvantage occurs. With such decor papers, it is known that it is particularly difficult to deliver them with a constant width. During the resin-treatment of the printed material web, more particularly paper width, of which the aforementioned decor paper is formed, this material, paper, respectively, becomes weaker and therefore more extensible. During transport through the resin-applying installation, different forces occur, due to which the paper is stretched somewhat. Up to now, it is particularly difficult to keep this stretching, which manifests itself in the width of the material web more than in the length thereof, precisely under control. This results in that a pattern present in the decor, in function of the stretching that manifests itself, will be more or less widened. As the pattern on a press plate, however, is unalterably fixed, it is clear that, in function of said stretching, the impressed pattern may deviate from the printed pattern to a minor or major extent. In order to exclude major deviations, it is known to produce two or three press plates, each with a relief with a similar pattern or motif, however, differing somewhat in mutual respect in that the patterns or motifs are stretched somewhat more or less, respectively, in respect to each other. In function of each batch of produced material sheets, then the press plate that best matches the decor can be used for pressing. However, it is disadvantageous that manufacturing two or more of such large press plates with mutually more or less stretched relief patterns is quite expensive.